Wear resistant cast iron



1967 G. E. WILLEY ETAL 3,295,965

WEAR RESISTANT CAST IRON Filed Sept. 30, 1963 INVENTORS GORDON E WILLEYBY FRANKLIN w. KELLAM United States Patent 3,295,965 WEAR RESISTANT CASTIRON Gordon E. Willey and Franklin W. Kellam, Thornhill, Ontario,Canada, assignors to Union Carbide Canada Limited, Toronto, Ontario,Canada, a corporation Filed Sept. 30, 1963, Ser. No. 312,772 5 Claims.(Cl. 75-125) The present invention relates to cast irons. Moreparticularly, the present invention relates to cast irons containingrelatively large amounts of manganese as an alloying constituent.

A substantial quantity of cast grinding ball and other castingsrequiring a high order of wear resistance have previously beenmanufactured from a cast iron containing from about 2.5 to 5 percentnickel as the predominant alloying constituent. While castings of thisalloy have been satisfactory, being strong and wear resistant, theincreasing price of nickel has imposed a significant economic penalty onits use.

It is therefore an object of the present invention to provide arelatively inexpensive, strong, wear resistant cast iron containinglittle or no nickel.

It is a further object of the present invention to provid a wearresistant cast iron containing little or no nickel and which has aBrinell Hardness of 500 or more.

Other objects will be apparent from the following description and claimstaken in conjunction with the single figure of the drawing which shows aphotomicrograph of a cast iron of the present invention.

A cast iron in accordance with the present invention has a compositionin the ranges shown in Table I.

It has been discovered, as part of the present invention, that by usingrelatively large alloying proportions of manganese in cast irons, and bycontrolling the proportions of silicon and carbon in specific ranges, astrong wear resistant cast iron material is obtained from which theusual nickel content can be eliminated in whole or in part withoutdetrimental effect, while providing significant economic benefit.

The microstructure of the alloy of the present invention consistsessentially of primary carbides in a matrix of martensite and ansteniteand the alloy of the present invention derives its beneficial propertiesfrom its characteristic structure which is at least 70 percentmartensite. The aforementioned structure imparts to the alloy ahardness, measured as Brinell Hardness Number, of 500 or more. Thestructure of the alloy of the present invention can be readilycontrasted with the pearlite-cementite structure of unalloyed white castiron.

The sturcture and resultant hardness of the alloy of the presentinvention is developed in a cast iron with a manganese content in therange of 3.5% to 12% when the silicon and carbon are in the range of0.4%0.7%, and 2.9%3.6% respectively.

If lesser amounts of manganese are used, or if the carbon or silicon areoutside the specified ranges, then a suitable hardness of 500 BHN orabove is not obtained nor is the desired structure present in thematerial.

With reference to the drawing, the single figure shows a photomicrograph(original magnification: 900x) of a cast iron in accordance with thepresent invention. The composition of the material shown in the drawingis Patented Jan. 3, 1967 3.86% Mn, 1.52% Cr, 1.37% Ni, 0.64% Si, 3.35%C, bal. Fe. In the photomicrograph, the numeral 1 indicates a mixture ofmartensite which appears as a continuous area with needle likeinclusions and anstenite in dendritic form. The white area 2 isanstenite and the gray islands 3, surrounded by anstenite, are primarycarbides.

In the preparation of the cast iron of the present invention,consideration is given to the manufacturing technique employed whenselecting the proportions of manganese and nickel (or copper) within theaforementioned ranges in order to obtain the desired structure andhardness.

For example, when using water cooled permanent metal molds, and when thecasting mass is small relative to the mold, i.e., the cooling of thecasting is relatively rapid, the manganese content can be selected fromthe lower part of the range. On the other hand, when the casting mass islarge and the permanent mold walls are relatively thin, or the moldedmaterial has low heat conductivity as in sand casting, the manganesecontent should be selected from the upper part of the range.

By way of illustration, in the manufacture of a l-3 inch diametergrinding ball using a water-cooled cast iron mold, 1 to 2 inches thick,between 3.5% and 4% manganese can be used. When casting the same ball ina sand mold, 1 to 2 inches thick, between 8% and 9% manganese should beused in order to obtain substantially the same structure and hardness.

Also, if larger diameter balls were cast in the same type molds, about4.0% to 5.0% manganese is recommended with the metal molds and 9.0% to11.0% manganese with sand molds.

In the practice of the present invention, when the manganese content ofthe cast iron is 6% or more, nickel can be eliminated entirely from thealloy. At lower manganese levels, however, between 0.5% and 1.5% in theaggregate of nickel and copper is required. That is to say, at the lowermanganese levels the alloy should contain between 0.5% and 1.5% nickel,or between 0.5% and 1.5% copper, or between 0.5% and 1.5% ofcopper+nickel. The selection of a particular aggregate value "in thisrange is made following the same considerations Table II PercentManganese 3.5 to 8 Nickel-l-Copper 0.5 to 1.5 Chromium 1 to 2.5 Silicon0.4 to 0.7 Carbon 2.9 to 3.6 Iron and incidental impurities Balance.

In preparing cast irons in accordance with the present inventionordinary practices can be followed and melting can be accomplished inmost furnaces used for the melting of cast iron. Such furnaces includecupola, air furnace, gas fired furnace, direct and indirect are electricfurnaces and induction types.

By way of illustration, the following Table III lists specificcompositions in the form of grinding balls having a BHN of 500 or moreand which are at least 70 percent 3 martensite. consists essentially ofprimary carbides in a matrix of martensite and austenite.

The microstructure of these compositions i 4 be eliminated in whole orin part with substantial savings without loss of hardness and wearresistance. The economic advantages of the present invention can be ap-T able III Composition Diameter of Balls Cast, Type Mould PercentPercent Percent Percent Percent Percent Inches Mn Or Ni Cu Si O 3.861.52 1.37 0.64 3.35 2.00 Cast; iron,water-cooled 3.98 1.38 0. 45 1. 030. 66 3.36 1. 50 Do. 4. 04 1. 45 0. 41 1.08 0. 60 3. 3s 1. 25 Do. 3.57 1. 70 0. 39 1. 07 0. 62 a. 32 3. Do.

*Balance iron.

In all examples, the mold wall thickness varied between preciated inview of the fact that at the present time,-the one and two inches, withthe thinner walls occurring in cost of nickel is to 8 times the cost ofmanganese. the molds used for larger balls. What is claimed is:

In order to maintain the best strength properties in the 1. A cast ironalloy consisting essentially of 3.5% to cast iron of this invention itis desirable that phosphorus 12% manganese; 1% to 2.5 chromium; (14% t0be maintained at a level not exceeding 0.15%. Also silicon; 2.9% to 3.6%carbon; up to 1.5% in the aggresince sulphur forms deleterious compoundswhen present gate of copper and nickel; not more than 0.15 phosinexcessive amounts and since sulphur is suspected to phorus; not morethan 0.1% sulfur; the balance iron and promote porosity through gaseousreaction with manganese," it is desirable that this element be kept aslow as possible, preferably below 0.05% and not exceeding about 0.10%.

The following example is provided to further illustrate the presentinvention.

EXAMPLE A heat of 2 inch diameter grinding balls was produced using acupola furnace and cast iron wateracooled permanent molds having a wallthickness of 1 to 2 inches. The charge was 220 pounds of steel scrap, 50pounds of manganese steel scrap containing 12% manganese, 140 pounds ofgrinding ball remelts containing 2.7% nickel and 1.40% chromium, 45pounds of gray iron scrap, 1 pound of 75% ferrosilicon, 7 pounds ofhigh-carbon ferrochrome containing 65% chromium, 36 pounds of standardferromanganese containing 80% manganese, and 1 pound of nickel cathode.The coke addition between each metal charge was 90 pounds and a ladleaddition of 1 /2 ounces of aluminum was made for 500 pounds of product.

A chemical analysis of sample balls made from this heat showed manganese3.86%, nickel 1.37%, chromium 1.52%, silicon 0.64%, and carbon 3.35%. Asample ball was out, polished, etched, and examined under themicroscope. The material contained about 75 percent martensite and themicrostructure consisted essentially of primary carbides in a matrix ofmartensite and austenite. The same ball was subjected to BrinellHardness measurement and exhibited a Brinell Hardness number of 500.

From the foregoing description it can be seen that the present inventionprovides a manganese containing cast iron in which the expensive nickelalloying ingredient can incidental impurities.

2. A cast iron alloy consisting essentially of 6% to 12% manganese; 1%to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 36% carbon; not morethan 0.15% of phosphorus; not more than 0.1% sulfur; the balance ironand incidental impurities.

3. A cast iron alloy consisting essentially of 3.5% to 8% manganese; 1%to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 3.6% carbon; 0.5% to 1.5in the aggregate of copper and nickel; not more than 0.15% phosphorus;not more than 0.05% sulfur; the balance iron and incidental impurities.

4. A cast iron alloy consisting essentially of 3.5% to 8% manganese; 1%to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 3.6% carbon; 0.5% to1.5% nickel; not more than 0.15% phosphorus; not more than 0.05 s'ulfur;the balance iron and incidental impurities.

5. A cast iron alloy consisting essentially of 3.5 to 8% manganese; 1%to 2.5% chromium; 0.4% to 0.7% silicon; 2.9% to 3.6% carbon; 0.5% to1.5% copper; not more than 0.15 phosphorus; not more than 0.05 sulfur;the balance iron and incidental impurities.

References Cited by the Examiner UNITED STATES PATENTS 2,129,683 9/1938Gontermann 7s 12s x FOREIGN PATENTS 450,089 7/1936 Great Britain.464,901 4/1937 Great Britain. 467,159 .6/1937 Great Britain. 468,4247/1937 Great Britain.

DAVID L. RECK, Primary Examiner.

' P. WEI-NSTEIN, Assistant Examiner.

1. A CAST IRON ALLOY CONSISTING ESSENTIALLY OF 3.5% TO 12% MANGANESE; 1%TO 2.5% CHROMIUM; 0.4% TO 0.7% SILICON; 2.9% TO 3.6% CARBON; UP TO 1.5%IN THE AGGREGATE OF COPPER AND NICKEL; NOT MORE THAN 0.15% PHOSPHORUS;NOT MORE THAN 0.1% SULFUR; THE BALANCE IRON AND INCIDENTAL IMPURITIES.